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Chemical Engineering Science

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ISSN (Print) 0009-2509
Published by Elsevier

[2565 journals]

A porous media model for blood flow within reticulated foam
- Abstract: Publication date: 9 August 2013
  Source:Chemical Engineering Science, Volume 99
  Author(s): J.M. Ortega
  A porous media model is developed for non-Newtonian blood flow through reticulated foam at Reynolds numbers ranging from 10−8 to 10. This empirical model effectively divides the pressure gradient versus flow speed curve into three regimes, in which either the non-Newtonian viscous forces, the Newtonian viscous forces, or the inertial fluid forces are most prevalent. When compared to simulation data of blood flow through two reticulated foam geometries, the model adequately captures the pressure gradient within all three regimes, especially that within the Newtonian regime where blood transitions from a power-law to a constant viscosity fluid.
  
  PubDate: 2013-06-15T13:18:08Z
Predicting fluid penetration during slot die coating onto porous substrates
- Abstract: Publication date: 9 August 2013
  Source:Chemical Engineering Science, Volume 99
  Author(s): Xiaoyu Ding , Thomas F. Fuller , Tequila A.L. Harris
  Slot die coating onto porous media is a distinct field in the coating industry and has broad applications. One important technical issue related to coating porous media is how to predict and control the fluid penetration depth, which directly affects the appearance, properties, and performance of the resulting material. Up to now, the analytical relationship between processing parameters and the final penetration depth are still not well understood. Existing modeling work either uses oversimplified assumption of pressure distribution in the coating bead, or does not provide a simple expression to predict the penetration depth and often requires a complex calculation procedure. Furthermore, previous models are limited to Newtonian fluids. In this study, new computational fluid dynamics (CFD) and analytical models to study the penetration of fluid into porous media during slot die coating were developed for Newtonian and non-Newtonian fluids. Penetration driven by the pressure in coating bead was considered in these models. To this end, basic analytical models that can easily and rapidly calculate the penetration depth were developed and the results were compared to CFD models. It was found that there exists good agreement between the analytical and CFD models when coating Newtonian and non-Newtonian fluids, having an overall relative error of less than 6% and ranging between 12–26%, respectively. Results from a parametric study, when coating Newtonian fluids, showed that viscosity has a negligible effect on the penetration depth; whereas coating speed, flow rate, permeability and porosity are more important. Based on the experimental analysis, similar trends exist for the measured and predicted values of the penetration depth when coating non-Newtonian fluids.
  
  PubDate: 2013-06-15T13:18:08Z
Lattice-Boltzmann simulation of fluid flow through packed beds of uniform spheres: Effect of porosity
- Abstract: Publication date: 9 August 2013
  Source:Chemical Engineering Science, Volume 99
  Author(s): L.W. Rong , K.J. Dong , A.B. Yu
  Fluid flow through packed beds of uniform spheres is studied by a parallel lattice-Boltzmann (LB) model. The packed beds are obtained from simulations based on discrete element methods and have a wide porosity range. The LB model is specially designed for particle systems and is validated by comparing the simulated and measured results under different conditions. The validated model is then used to study the effect of porosity on the internal fluid flow and quantify the drag force on particles in packed beds. The results suggest that both the Reynolds number and packing structure significantly affect the fluid velocity distribution. A correlation is demonstrated between the packing structure and the velocity distribution, especially for flows at low Reynolds numbers. Beds with large porosity subjected to relatively large (e.g. moderate) Reynolds numbers are prone to display a secondary peak in the probability distribution of the normalized velocity. The interaction forces between particles and fluid in packed beds are examined. As a result of the non-uniform structure and flow, the drag force on a single particle varies giving a probability distribution. Based on the simulated results, a new equation is proposed to estimate the mean drag force on particles, which is more accurate than the correlations in the literature.
  
  PubDate: 2013-06-15T13:18:08Z
Recyclable homogeneous catalyst for the hydroesterification of methyl oleate in thermomorphic solvent systems
- Abstract: Publication date: 9 August 2013
  Source:Chemical Engineering Science, Volume 99
  Author(s): A. Behr , A.J. Vorholt , N. Rentmeister
  In the development of commodity markets alternatives to fossil resources are of high interest. One alternative is the usage of oleo compounds. In this paper an atom economic hydroesterification of methyl oleate to linear and branched diesters is described. The selectivity to linear or branched products can be influenced by reaction parameters. These diesters can be used in polymers, plasticizers, lubricants or to adjust crystallinity in these materials. To the best of our knowledge we provide the first efficient catalyst recycling in the hydroesterification of fatty compounds. The catalyst system of palladium and XANTphos proved to be very stable. Products with the tough palladium XANTphos catalyst are mostly branched, while the selectivity to linear products can be influenced by temperature, carbon monoxide pressure and choice of solvent up to 64%. A high selectivity of 94% towards branched products was obtained if no solvent was used. Separation of products and catalyst was realised using thermomorphic solvent systems (TMS). The catalyst was recycled in a methanol/decane system with low leaching values. A recycling of the catalyst phase was conducted three times with no significant activity loss.
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  PubDate: 2013-06-15T13:18:08Z
High gradient magnetic separation of catalyst/wax mixture in Fischer–Tropsch synthesis: Modeling and experimental study
- Abstract: Publication date: 9 August 2013
  Source:Chemical Engineering Science, Volume 99
  Author(s): Jinli Zhang , Ziyang Feng , Xiaoqiang Jia , Mailin Liang , Zhuowu Men , Yu Zhang , Yifeng Bu , Wei Li
  Separation of magnetic catalyst particles from the wax stream in Fischer–Tropsch synthesis (FTS) process is one of the most important challenges for exploring FTS slurry bubble column reactors. In the present work, we studied the separation efficiency of magnetic catalytic particles from FTS wax using high gradient magnetic separation (HGMS), and the three-dimensional mathematical models were established to describe the magnetic field and magnetic force distribution with multi-wires for HGMS. The calculation results indicated that the distributions of magnetic field and magnetic force in HGMS were significantly related to the matrix arrangement patterns and the background uniform external magnetic field strength. The wire interval, the axial distance between matrices, the arrangement angle between matrices and the external magnetic field strength were investigated using the established models. Based on the experimental optimization, the magnetic iron content of the catalyst/wax mixture can be reduced to less than 30ppm through HGMS, with the separation efficiency higher than 99.77% for iron particles.
  
  PubDate: 2013-06-15T13:18:08Z
Analysis of power formulations for the thawing of frozen wood using microwave energy
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Erchiqui Fouad
  This paper addresses the thawing of frozen wood by micro wave. We consider two power formulations for the absorbed energy: the correct power dissipation computed from Maxwell's equations and Lambert's power law equation. The critical thickness above which the two formulations are approximately equivalent is characterized as an exponential-hyperbolic function of frequency and temperature. Four Canadian eastern wood species are used: trembling aspen (Populus tremuloides), yellow birch (Betula alleghaniensis), white birch (Betula paperyfera), and sugar maple (Acer saccharum). The nonlinear heat conduction problem involving phase changes such as wood freezing is solved by a volumetric specific enthalpy-based finite element method. Dielectric and thermophysical properties are functions of temperature and moisture content. For illustration purposes, we considered the thawing of frozen trembling aspen wood.
  
  PubDate: 2013-06-15T13:18:08Z
Large-scale CFD–DEM simulations of fluidized granular systems
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Dalibor Jajcevic , Eva Siegmann , Charles Radeke , Johannes G. Khinast
  The combination of Computational Fluid Dynamics (CFD) and Discrete Element Model (DEM) is a powerful tool for studying fluidized particulate systems and granular flows. In DEM, the individual interaction forces between particles are treated on a particle–particle pair basis, and therefore, this method is computational expensive. In addition, the CFD-calculation of the fluid flow increases the computational effort. Thus, current CFD–DEM simulations are limited to systems with particle numbers not exceeding 105. In order to simulate realistic systems, the recently available Compute Unified Device Architecture (CUDA) technology can be applied, which can perform massively-parallel DEM-simulations with several million particles on a single desk-side Graphics Processing Unit (GPU). The objective of this work is to present a new hybrid approach to solve CFD–DEM problems in gas–solid fluidized beds systems applying an efficient coupling method suitable for large-scale simulations. We are using the CUDA technology for the particle simulation and introducing a coupling methodology with a commercial CFD-code. The coupling method between a CFD-code, running on the CPU and our CUDA-based DEM-code running on the GPU, is introduced and discussed. The numerical results are compared to the CFD–DEM and the experimental results of Van Buijtenen et al. (2011). A good agreement was achieved. Finally, fluidized system simulations with up to 25 million particles are presented, which is an unprecented number.
  
  PubDate: 2013-06-15T13:18:08Z
Spreading of steadily-discharged oil on water in the viscous-gravity stage
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Rachid Chebbi
  The second stage of oil spreading on water, in which gravity forces promote spreading against the resisting viscous effects, is investigated using a similarity solution in combination with the integral boundary layer approach in the case where oil is discharged at a constant rate. Analytical solutions near the leading edge and the origin are developed, and used to start integration in both unidirectional and axisymmetric cases of spreading to provide a solution for the oil thickness, the oil velocity, and the boundary-layer thickness profiles. The existence of a singularity during integration required “matching” of two solutions originating from the leading edge and the origin. This led to the spreading law prefactor for the unidirectional spreading case. The prefactor reached with a simplified approach in a published theoretical work is found consistent with the present investigation value obtained based on a detailed analysis of the boundary layer in the water phase. The unidirectional spreading results are compared with the constant oil volume case. “Matching” was not possible in the axisymmetric spreading case, which is attributed to the infinite velocity at the origin, as given by the asymptotic solution. The analysis suggests the need for additional theoretical investigations in the axisymmetric spreading case. The order of magnitude analysis shows the need for further experimental work for both spreading geometries to ensure surface tension forces are negligible, which can be achieved by using sufficiently large oil discharge rates.
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  PubDate: 2013-06-15T13:18:08Z
A priori prediction of aggregation efficiency and rate constant for fluidized bed melt granulation
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Kel W. Chua , Yassir T. Makkawi , Michael J. Hounslow
  This paper presents a predictive aggregation rate model for spray fluidized bed melt granulation. The aggregation rate constant was derived from probability analysis of particle–droplet contact combined with time scale analysis of droplet solidification and granule–granule collision rates. The latter was obtained using the principles of kinetic theory of granular flow (KTGF). The predicted aggregation rate constants were validated by comparison with reported experimental data for a range of binder spray rate, binder droplet size and operating granulator temperature. The developed model is particularly useful for predicting particle size distributions and growth using population balance equations (PBEs).
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  PubDate: 2013-06-15T13:18:08Z
Thermal analysis of exothermic process in a magnesium hydride reactor with porous metals
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): D. Shen , C.Y. Zhao
  Compared with sensible and latent heat storage, thermochemical heat storage has the advantages of high storage capacity, low storage loss, etc., which make it become a most promising candidate for heat storage. Among numerous materials used for thermochemical heat storage, magnesium based materials are abundant, inexpensive and have a high storage density, therefore they have attracted extensive investigations. In this paper a two dimensional mathematical model for the heat releasing process of the Mg/MgH2 system was established to study the transient heat and mass transfer process. The results show that the effective heat transfer is the key factor influencing the output power. With the addition of metal foams, the effective thermal conductivity has a significant promotion, and thereby shortening the reaction time and improving the output power. A parametric study was conducted to examine the optimal conditions for the highest output power and a sensitivity analysis was performed to evaluate the various factors influencing the reaction time.
  
  PubDate: 2013-06-15T13:18:08Z
Optimal design and operation of polymer electrolyte membrane reactors for pure hydrogen production
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Seyyed Mohsen Mousavi Ehteshami , Siew Hwa Chan
  Carbon monoxide (CO) in the hydrogen (H2) stream diminishes the performance of a low-temperature polymer electrolyte membrane (PEM) fuel cell. An on-board CO removal unit is essential in any fuel processor system to be developed for production of hydrogen with low CO concentration (<10ppm). Low process temperature (80°C or lower) and pressure are critical for such a gas clean-up unit. The existing gas clean-up units operate at high temperatures and pressures and often require on-board oxygen or air supply for CO oxidation. An attractive solution for on-board/site production of pure hydrogen is the electrochemical approach. This method removes the CO molecules in the synthetic gas stream after they have been adsorbed onto the catalyst surface in the anode side of a polymer electrolyte membrane reactor. In this process, some additional hydrogen is also produced through the water-gas shift reaction at the cathode side of the reactor offsetting the energy required to drive the electrolysis. In this study, through a parametric study, the optimal geometrical design and operation conditions of the CO removal reactor are determined with an attempt of maximizing the adsorption capacity and minimizing the catalyst consumption.
  
  PubDate: 2013-06-15T13:18:08Z
Entropy generation analysis of H2/air premixed flame in micro-combustors with heat recuperation
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Dongyue Jiang , Wenming Yang , Kian Jon Chua
  A theoretical analysis on entropy generation in H2/air premixed flame is presented. The entropy transport equation is employed to evaluate the entropy generation rate caused by various irreversible processes such as chemical reaction, conduction, mass diffusion and viscous dissipation. The model is applied for premixed flames in a confined geometry under different inlet flow velocity levels and H2/air equivalence ratios. Comparisons between the combustors with and without heat recuperation are done in terms of specific and total rate of entropy generation. It is found that a higher flow velocity and higher H2/air equivalence ratio will increase the rate of entropy generation. The usage of heat recuperator decreases the rate of entropy generation which results in lower exergy loss.
  
  PubDate: 2013-06-15T13:18:08Z
Kinetics of micellar catalysis on oxidation of p-anisaldehyde to p-anisic acid in aqueous medium at room temperature
- Abstract: Publication date: 9 August 2013
  Source:Chemical Engineering Science, Volume 99
  Author(s): Rumpa Saha , Aniruddha Ghosh , Bidyut Saha
  Oxidation of p-anisaldehyde by chromic acid produces p-anisic acid under kinetic condition [p-anisaldehyde]T≫[Cr(VI)]T. This oxidation reaction is performed also in presence of micellar catalysts in aqueous media at room temperature. The progress of the reaction is monitored spectrophotometrically by following the decay of Cr(VI) at 450nm wavelength. The product is confirmed by 1H NMR spectroscopy. Anionic surfactant sodium dodecyl sulfate (SDS) accelerated the reaction almost three-fold compared to uncatalyzed path, whereas cationic surfactant N-cetylpyridinium chloride (CPC) and neutral surfactant triton-X-100 (TX-100) inhibited the reaction.
  
  PubDate: 2013-06-15T13:18:08Z
Comment on “QSPR approach for determination of parachor of non-electrolyte organic compounds [Gharagheizi et al., 2011. Chem. Eng. Sci. 66, 2959–2967]”
- Abstract: Publication date: 9 August 2013
  Source:Chemical Engineering Science, Volume 99
  Author(s): Sierra Rayne
  
  PubDate: 2013-06-15T13:18:08Z
Extension to nonlinear adsorption isotherms of exact analytical solutions to mass diffusion problems
- Abstract: Publication date: 9 August 2013
  Source:Chemical Engineering Science, Volume 99
  Author(s): Daniel Goujot , Olivier Vitrac
  Analytical solutions with algebraic expressions are proposed for one-dimensional nonlinear mass diffusion problems. The solutions proposed to solve sorption/desorption problems are rigorously exact for piecewise linear isotherms. They provide an efficient methodology to devise analytical solutions to nonlinear isotherms, and instantly time-varying boundary conditions, with arbitrary accuracy. An exact solution is calculated for each linear piece of the isotherm and is then propagated iteratively to the next linear piece. For end-user convenience and efficiency, three exact analytical expansions are proposed: a new short and intermediate contact time expansion obtained using the Laplace transform (erfc solution), a modified version of Eq. (33) in Sagiv (2002) with improved stability (Sagiv solution), and a new expansion with a decreasing energy norm (energy solution). All expansions are compared in terms of their accuracy and number of terms for typical nonlinear isotherms, mass Biot numbers and volume ratios covering a broad range of applications. When the thermodynamic conditions are changed at the interface, only the “erfc” and the “energy” solutions retain overall accuracy (machine precision) with few terms (<30). New strategies to enable the simultaneous estimation of diffusion coefficients, isotherms and mass Biot numbers are finally derived.
  
  PubDate: 2013-06-15T13:18:08Z
Simultaneous synthesis approaches for cost-effective heat exchanger networks
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Ke Feng Huang , Iftekhar A. Karimi
  The chemical process industry is a major user of energy. Energy recovery via heat integration is a long established practice in this industry. The existing mathematical programming based approaches for simultaneous heat exchanger network synthesis (HENS) have employed two superstructures (Floudas et al., 1986. AIChE J. 32, 276–290; Yee and Grossmann, 1990. Comput. Chem. Eng. 14, 1165–1184) with well-documented limitations. We propose two new superstructures and corresponding mixed integer nonlinear programming (MINLP) models for simultaneous HENS. While one superstructure is multistage, match-centric, and combines the strengths of existing superstructures, the other has no stages, is exchanger-centric, and is entirely distinct. Both superstructures allow cross flows, cyclic matching, series matches on a substream, multiple utilities, and utility placement at any stage. They admit several network configurations that the existing superstructures do not. We also present novel ways of modeling temperature changes and approaches. We demonstrate significant advantages of our first model by obtaining networks with lower total annualized costs than those reported for seven literature examples. The second model, however, requires further work to improve computational efficiency. While our work improves the quality of HENS solutions, solution speed and global optimality are challenges that need further work.
  
  PubDate: 2013-06-11T15:15:24Z
Adsorption and separation of CH4/H2 in MIL-101s by molecular simulation study
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Defei Liu , Y.S. Lin , Zhong Li , Hongxia Xi
  MIL-101s offer potential application for CH4/H2 adsorption separation owing to its high porosity and excellent chemical stability. In this work, the grand canonical Monte Carlo method was employed to study the adsorption and separation of CH4/H2 on a novel series of MIL-101s materials, such as MIL-101, MIL-101_NDC and new constructed MIL-101_R7-BDC. The simulation results showed that CH4 was preferentially adsorbed over H2 in all MIL-101s. The adsorption capacities of pure CH4 and H2 on MIL-101_NDC were much higher than that in the other two MIL-101s, due to its largest S acc (accessible surface area) and V p (pore volume). The adsorption-site results suggested that the super-tetrahedras were the main adsorption site for CH4 molecules in all studied MIL-101s. Moreover, the additional benzene rings in MIL-101_R7-BDC introduced several new CH4 adsorption sites which were close to the edge of large and small cages. Finally, we found that MIL-101_R7-BDC had the highest CH4 selectivity. CH4 selectivity of MIL-101s was significantly affected by Δq st (adsorption heat) and S acc (accessible surface area) in terms of different organic ligands.
  
  PubDate: 2013-06-11T15:15:24Z
Transition from turbulent to transitional flow in the top half of a stirred tank
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Márcio B. Machado , Kevin J. Bittorf , Vesselina T. Roussinova , Suzanne M. Kresta
  The limits of fully developed turbulence are defined in the wall jet and in the recirculation flow for three different impeller geometries: A310, HE3 and PBTD. At two different tank scales, mean velocity profiles in both the wall jet and the recirculation flow were measured to determine whether the condition of fully turbulent self-similarity is satisfied. Higher impeller Reynolds numbers are able to keep the flow fully turbulent higher in the tank. In addition to the expected effect of impeller Reynolds number, the fluid also affected the flow regime. Measurements in a pilot scale stirred tank gave similar results. Although the power number is often constant for Re>20 000, an impeller Re≥300 000 is required to keep the flow in the fully turbulent regime in the top third of the tank and in the recirculation zone.
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  PubDate: 2013-06-11T15:15:24Z
Analysis on the onset of buoyancy-driven convection in a fluid-saturated porous medium heated uniformly from below
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Min Chan Kim , Chang Kyun Choi
  The onset of convective motion in an initially quiescent, horizontal isotropic porous layer is analyzed theoretically. Using linear theory, the stability equations are obtained with and without the quasi-steady state approximation (QSSA). They are solved by expanding the disturbances as a series of orthogonal functions. Initial value problem analyses also are conducted, and their results are compared with the eigenanalysis and the QSSA. For the large Darcy–Rayleigh number R a D , the critical time of the onset of convection is found to be τ c = 11.74 R a D − 1 with the critical wavenumber k c = 0.29 R a D 1 / 2 . Based on linear analyses, numerical simulations are conducted to consider nonlinear effects. The nonlinear analysis using the Fourier spectral method and the finite volume method reproduces the linear stability limit obtained theoretically. From the present nonlinear analysis, it is shown that manifest convection is observed experimentally from τ m = 51.42 R a D − 1 .
  
  PubDate: 2013-06-11T15:15:24Z
Physico-chemical properties of bile salt-Tween 80 mixed micelles in the viewpoint of regular solution theory
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Mihalj Poša , Dejan Ćirin , Veljko Krstonošić
  In this work mixed micelles of Na salts of bile acids and Tween 80 are studied. In the experiment, number and orientation of OH and oxo groups in the steroid skeleton of bile acid anion varies. In every investigated mixture, mole fraction of Tween 80 (α) varies from 0.05 to 0.5 of the total surfactant concentration. Critical micelle concentrations of binary surfactant mixtures are determined by tensiometric and conductometric methods (modified Philips method of data processing). By employing regular solution theory for every studied binary surfactant mixture, values of interaction coefficient (β 1,2) are determined. Based on the obtained β 1,2 values, investigated bile acid anions form two groups. Group I consists of bile acids having only OH groups attached to the steroid skeleton. Characteristics of mixed micelles of this group are negative values of β 1,2 for α to 0.1 (synergistic effect between different types of the micelle building units), and positive values of β 1,2 for α over 0.1 (antagonistic effect). This change of sign of β 1,2 as a function of α can be explained by phase transformation in mixed micelle as a pseudophase, and due to rigid geometry of cis-oleic residue of Tween 80. Group II is formed of bile acid anions having one or more oxo groups in the steroid skeleton. Mixed micelles of Tween 80 and group II of bile acid anions are characterized by positive β 1,2 values in the whole investigated range of α. Based on the intensity measurements at different temperatures of first (I 1) and third (I 3) vibrational bands of pyrene (probe molecule) emission spectrum as a function of total surfactant concentration, it can be concluded that mixed micelles having Tween 80 are less rigid than mixed micelles having Tween 40. This also indicates that in hydrophobic domain of mixed micelles, cis-oleic residues are more difficult to pack together compared to the palmitic residues of Tween 40.
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  PubDate: 2013-06-07T13:05:01Z
Study of two phase thermal stratification in cylindrical vessels: CFD simulations and PIV measurements
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Mayurkumar S. Gandhi , Jyeshtharaj B. Joshi , Pallippattu K. Vijayan
  Buoyancy induced flow and heat transfer are important phenomena in a wide range of engineering systems including electronics and photovoltaics cooling, thermosiphon and hydrosiphon heat exchangers, solar-thermal heat absorbers, passive decay heat removal systems, etc. Such systems are vulnerable to thermal stratification, which can significantly compromise performance. The objective of the present work is to study different passive heat transfer systems, characterized by an absence of active components such as pumps. We have investigated two phase (boiling) natural convection, in order to find the ways to modify the extent of thermal stratification. We have considered a base case of a cylindrical tank, fitted with a central heating tube constituting the heat transfer surface. In addition, a large number of design modifications have been considered. The flow field and the corresponding stratification have been compared with the base case. We have considered the following design modifications to this system: (a) changing the ratio of heat transfer length (of the central heating tube) to liquid height (L T /H), (b) provision of different draft tube designs which act as a chimney, and (c) attachment of circular horizontal baffles (both non-conducting and conducting). The investigations were made using Computational Fluid Dynamic (CFD) simulations implemented via the commercial software FLUENT-6.3. The CFD predictions have been compared with the experimental measurement of flow field obtained using Particle Image Velocimetry (PIV) and temperature measurements using thermocouples. The extents of thermal stratification and mixing have been investigated for a wide range of Rayleigh numbers (9.37×1010≤Ra≤5.57×1013). A good agreement has been obtained between the CFD simulations and the experimental measurements. The results show that the use of conducting baffles with appropriate size, number, and location can significantly reduce the stratification and concomitantly enhance the extent of mixing through modifications in the flow fields and heat flux.
  
  PubDate: 2013-06-07T13:05:01Z
Experimental study on the dynamics of binary fuel droplet impacts on a heated surface
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): E. Kompinsky , G. Dolan , E. Sher
  The dynamics of a binary fuel droplet impinging on a heated surface was studied experimentally. The fuel droplets consisted of a mixture of n-hexane and n-decane fuels which have significantly different boiling temperatures. We show that the impact regimes obtained with binary fuel droplets are significantly different from those obtained with single component droplets, especially when surface temperatures exceeded the boiling point of n-hexane, the more volatile component in the mixture. Six distinctive impact regimes were identified and classified for binary and single component droplets’ cases. Some of them were applicable for both cases, while others proved to be unique for only one of them. In addition, the effect of the droplet's impact velocity on the subsequent impact regime was examined. It was found that an increased droplet's impact velocity actually lowered the surface temperatures characterizing the specific impact regime. Furthermore, a droplet breakup phenomenon which takes place when a droplet impacts a hot surface was also examined. Minimal critical surface temperature needed for a droplet breakup was found. This temperature appears to be independent of impact velocity above a certain value (within the examined range).
  
  PubDate: 2013-06-07T13:05:01Z
Upscaling and microstructural analysis of the flow-structure relation perpendicular to random, parallel fiber arrays
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): K. Yazdchi , S. Luding
  Owing largely to multiscale heterogeneity in the underlying fibrous structure, the physics of fluid flow in and through fibrous media is incredibly complex. Using fully resolved finite element (FE) simulations of Newtonian, incompressible fluid flow perpendicular to the fibers, the macroscopic permeability is calculated in the creeping flow regime for arrays of random, ideal, perfectly parallel fibers. On the micro-scale, several order parameters, based on Voronoi and Delaunay tessellations, are introduced to characterize the structure of the randomly distributed, parallel, non-overlapping fiber arrays. In particular, by analyzing the mean and the distribution of the topological and metrical properties of Voronoi polygons, we observe a smooth transition from disorder to (partial) order with decreasing porosity, i.e., increasing packing fraction. On the macro-scale, the effect of fiber arrangement and local crystalline regions on the macroscopic permeability is discussed. For both permeability and local bond orientation order parameter, the deviation from a fully random configuration can be well represented by an exponential term as function of the mean gap width, which links the macro- and the micro-scales. Finally, we verify the validity of the, originally, macroscopic Darcy's law at various smaller length scales, using local Voronoi/Delaunay cells as well as uniform square cells, for a wide range of porosities. At various cell sizes, the average value and probability distributions of macroscopic quantities, such as superficial fluid velocity, pressure gradient or permeability, are obtained. These values are compared with the macroscopic permeability in Darcy's law, as the basis for a hierarchical upscaling methodology.
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  PubDate: 2013-06-07T13:05:01Z
Development of simultaneous membrane distillation–crystallization (SMDC) technology for treatment of saturated brine
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Felinia Edwie , Tai-Shung Chung
  We have developed the simultaneous membrane distillation–crystallization (SMDC) hybrid desalination technology for the concurrent productions of pure water and salt crystal from the saturated brine solutions. The effects of feed temperature variation from 40°C to 70°C on the SMDC performance in terms of membrane flux and kinetics of NaCl crystallization have been investigated. Increasing feed temperature increases membrane flux but the flux declines rapidly with time at higher feed temperatures (60°C and 70°C) due to the occurrences of membrane scaling and wetting facilitated by salt oversaturation at the boundary layer. In order to prevent salt oversaturation, we have calculated the critical fluxes at different Reynolds numbers and crystallizer temperatures. For instance, the critical fluxes when the feed temperature is 70°C increase from 5kgm−2 h−1 to 20kgm−2 h−1 for the laminar and turbulent flows, respectively. By keeping the membrane flux lower than the critical flux, a stable membrane performance during a continuous SMDC operation over the period of 5000min has been achieved. Increasing feed temperature also increases the yield of NaCl crystals from 7.5kgperm3 solution to 34kgperm3 for feed temperatures of 40°C and 70°C after 200min operation, respectively. However, the average crystal sizes decrease from 87.40µm to 48.82µm with increasing feed temperatures from 40°C to 70°C due to a higher nucleation rate at a higher degree of supersaturation. Regardless of the feed temperature, the NaCl crystals are in a uniform cubical shape with the coefficient of variations which are in the range of 30–38% that implies a narrow dispersion.
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  PubDate: 2013-06-07T13:05:01Z
Table of Contents
- Abstract: Publication date: 28 June 2013
  Source:Chemical Engineering Science, Volume 97
  
  PubDate: 2013-06-07T13:05:01Z
Template-directed synthesis of hollow silica beads by an interfacial sol–gel route
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Kaifeng Du , Xudong Cui , Bin Tang
  Hollow silica beads with controllable shell thickness are successfully fabricated by means of an improved template-directed interfacial sol–gel polymerization. Templates made by the proteins-entrapped agarose beads with strong functionalities such as preventing collapse and unwanted permeation from shells allow us to construct desired hollow beads. Our investigations show that the resulting beads are nearly uniform with an average cavity size of 210µm. The beads are with less shrinkage and good surface roughness when the cores are completely removed. Shell thickness can be tuned from 1 to 9µm by simply altering the volume ratio of silica precursors to solvent from 0.02 to 0.15. The mechanical stability increases with shell thickness under compression tests. The pore size of amorphous shells is about 5nm and the specific surface area is about 315m2 g−1, which is ready for some specific applications. Besides the importance of material selections we stressed in this work, it is worth to note that our fabrication can be in a batch mode and thus might open a way to synthesize other inorganic hollow beads, which already found applications in the inertial confinement fusion experiments etc., to overcome some mass production issues.
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  PubDate: 2013-06-07T13:05:01Z
Experimental study of the bubble size distribution in a pseudo-2D bubble column
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Y.M. Lau , K. Thiruvalluvan Sujatha , M. Gaeini , N.G. Deen , J.A.M. Kuipers
  This work presents an experimental study of the bubble size distribution of a bubbly flow using digital image analysis (DIA). In order to facilitate the image measurement technique a pseudo-2D bubble column is chosen for the experiments. To obtain well-defined inlet conditions a gas sparger, consisting of 20 needles, is used. By employing DIA, the bubble size distribution (BSD) has been measured for a range of superficial gas velocities. The resulting BSD's are expressed in terms of a probability density function (PDF). For low superficial gas velocities of 5 and 10mm/s the PDF has a unimodal shape, while for higher superficial gas velocities of 15 and 20mm/s the PDF has a bimodal shape. The effects of coalescence and break-up of bubbles are visible by evaluating the changes of the resulting BSDs for increasing superficial gas velocity. A comparison of gas hold-ups is made between the calculated BSD and the liquid expansion height. This comparison shows how well the BSD obtained with DIA describes the actual gas hold-up in the column.
  Graphical abstract Highlights
  
  PubDate: 2013-06-07T13:05:01Z
Carbon dioxide gas hydrate crystallization in porous silica gel particles partially saturated with a surfactant solution
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Christophe Dicharry , Christophe Duchateau , Halim Asbaï , Daniel Broseta , Jean-Philippe Torré
  This paper reports on investigations into the way carbon dioxide (CO2) hydrate forms in porous silica gel partially saturated with pure water or with a surfactant solution. The experiments, conducted at two different temperatures (278.2 and 279.2K) and under a loading pressure of 3.8MPa, used silica particles of different nominal pore diameters (30 and 100nm), saturated at 80% pore volume with pure water or with a 100ppm solution of either sodium dodecyl sulfate (SDS) or polyoxyethylenesorbitan monoleate (Tween-80). They were run following the “hydrate precursor method” developed in previous works (Duchateau et al., 2009, 2010) to form bulk hydrate under controlled subcooling conditions, and adapted for studying hydrate formation behavior in porous media. The work demonstrated that the successive hydrate formation and decomposition cycles involved in this method do not alter the pore size distribution in the porous media. At the two temperatures investigated, silica gel particles with a nominal pore diameter of 100nm proved better suited to comparing the CO2-hydrate formation behaviors: higher water-to-hydrate conversions (>90mol%) were effectively obtained for all the conditions tested making comparison of the results much easier. Of the two surfactants used, only SDS was found to produce a positive effect on both the hydrate formation kinetics and the amount of hydrate formed. Our visual observations of quiescent bulk systems (without porous silica gel) suggest that when SDS is present, CO2 hydrate forms not only at the w/g interface (where it occurs without SDS too), but also in the bulk water phase. This may explain the beneficial effect observed on the porous medium.
  
  PubDate: 2013-06-03T11:22:18Z
Evolution of dispersion along the extruder during the manufacture of polymer–organoclay nanocomposites
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): J.M. Barbas , A.V. Machado , J.A. Covas
  Although correlations between the final dispersion level of organoclay nanocomposites and melt mixing conditions in a twin screw extruder have been proposed, the actual lengthwise evolution of dispersion in these machines is still not well understood. Despite their practical importance such studies are difficult, due to the possibility of inducing degradation and/or morphology changes during material collection and/or sample preparation. This work uses on-line rheometry and in-line near-infrared spectroscopy (NIR) to monitor the evolution of dispersion of a PP/PP-g-MA/organoclay system along the axis of twin screw extruder. Regardless of the screw profile utilised, dispersion develops quickly in the first part of the machine, and then it levels-off or decreases, even if the final dispersion levels are significant. In order to validate this data, Scanning Transmitted Electron Microscopy (STEM), X-ray diffraction (XRD) and mid-FT-IR analyses are carried out on samples collected from the same locations where the on-line/in-line measurements were performed. The results confirmed the previous measurements. Thermogravimetric analysis (TGA) and Time of Flight-Secondary Ion Mass Spectrometry (TOF-SIMS) on clay, matrix and nanocomposite showed that thermal degradation of the clay surfactant and of the polymer matrix could contribute to the observed dispersion reversal.
  Graphical abstract
  
  PubDate: 2013-06-03T11:22:18Z
Particle-train dynamics in curved microfluidic channels at intermediate Reynolds numbers
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): X. Zhang , A.S. Kim , D. Garmire
  A picture of the continuous transition of particle behavior with increasing Reynolds number (Re) is presented by the study of equilibrium positions andparticle array configurations in curved microfluidic channels. Particles with different diameters (d=10– 20 μ m ) are studied flowing in curved channels of different heights (h=50 and 100 μ m ).The study focuses on an intermediate range (Re=10–40) where the competing inertial force and the Dean force result in complex phenomena which include particle train twisting, particle focusing in the same hybrid array, and the tendency of the smaller particles leading a hybrid array. These observations are coupled to numerical computations to further the quantitative understanding of the underlying physical systems. Three-dimensional finite-element modeling of the channel reveals the lateral flow-focusing position in the channel under varying Re. Dissipative hydrodynamic simulations describe the stability of each observed particle train configuration.
  
  PubDate: 2013-06-03T11:22:18Z
Modeling liquid–liquid and vapor–liquid equilibria for the hydrocarbon+N-formylmorpholine system using the CPA equation of state
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Hossein Mahmoudjanloo , Amir A. Izadpanah , Shahriar Osfouri , Amir H. Mohammadi
  In this communication, the capability of the CPA (Cubic-Plus-Association) equation of state (EoS) for modeling vapor–liquid and liquid–liquid equilibria of mixtures containing N-formylmorpholine (NFM), alkanes and aromatics in a wide temperature range is studied. First, the CPA EoS parameters for NFM are obtained using vapor pressure and saturated liquid density data. Then, the liquid–liquid equilibrium of binary mixtures of NFM and alkane and later the vapor–liquid equilibrium for systems containing NFM and aromatics is investigated to determine the best parameters and association scheme. It is shown that the use of 4C association scheme for NFM yields satisfactory results.
  
  PubDate: 2013-06-03T11:22:18Z
Unification of STN and RTN based models for short-term scheduling of batch plants with shared resources
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Munawar A. Shaik , Ramsagar Vooradi
  State-task-network (STN) and resource-task-network (RTN) representations are popularly used for formulating mathematical models of scheduling problems. In contrast to STN representation, RTN representation offers unified treatment for different resources such as processing and storage units, material states and utilities. In global-event (or single-time grid) based models processing tasks occurring in different units are aligned globally, hence, they explicitly do not distinguish handling of resources such as utilities and material states. While, unit-specific event (or multi-time grid) based models offer better computational performance due to requirement of lesser number of events, but there is no unified treatment for handling of utility or discrete resources due to heterogeneous location of events. Usually, global alignment is enforced for different tasks that use the same utility, while for material states unit-specific alignment is used. Hence, for unit-specific event-based models it is desirable to have a unified framework for handling of material states and utility resources, which, not only offers a unification of STN and RTN formulations, but, potentially can result in further reduction in the number of events required to find optimal solutions. In this work, we propose a unified framework and develop two unit-specific event-based approaches for STN and RTN representations by incorporating a novel resource balance that offers these two unifications. The key features of the proposed approach are: (i) all resources are treated in unified way for the first time, (ii) simplified handling of multiple orders using the concept of active task, (iii) handling of shared storage problems in non-aggregated storage tanks by considering explicit storage tasks. The proposed features are demonstrated on few benchmark examples from literature.
  
  PubDate: 2013-06-03T11:22:18Z
Flooding characteristics of an aqueous two-phase system in a counter-current Kühni-type column
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Sabine Rode , Alain Durand , Isabelle Mabille , Eric Favre
  The flooding behavior of an aqueous two-phase system was investigated using a laboratory-scale counter-current agitated Kühni-type column. Experimental flooding limits were compared to the literature which has been established for aqueous–organic two-phase systems. Although the density difference and interfacial tension in the aqueous two-phase system studied were beyond the values typically encountered in aqueous-organic systems, comparison to the existing literature allowed for a prediction of the onset of flooding. Thus existing estimation procedures of the mean Sauter droplet diameter and terminal droplet velocity can be applied to aqueous two-phase systems.
  
  PubDate: 2013-06-03T11:22:18Z
Preparation of novel anion exchangers from pine sawdust and bark, spruce bark, birch bark and peat for the removal of nitrate
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Anni Keränen , Tiina Leiviskä , Bao-Yu Gao , Osmo Hormi , Juha Tanskanen
  Novel anion exchangers were prepared from pine (Pinus sylvestris) sawdust and bark, spruce (Picea abies) bark, birch (Betula pubescens/Betula verrucosa) bark and peat for the removal of nitrate (NO3 −). Chemical modification was applied by means of epichlorohydrin, ethylenediamine and triethylamine in the presence of N,N-dimethylformamide (DMF). The materials were characterized in terms of elemental composition (C, H, N and O), chemical composition, BET surface area, FT-IR spectra and FESEM. Nitrogen (NO3 −–N) removal efficiency (%) was used as a performance indicator for the anion exchangers. Modified pine sawdust exhibited the best nitrate removal efficiency. Over 80% of NO3 −–N was removed at doses of >3g/l with a NO3 −–N concentration of 30mg/l. The removal efficiency of modified pine sawdust remained unchanged at pH 3–10. Maximum sorption capacities of 24.2–30.1mg/g were achieved for NO3 −–N, which were very good compared to the literature values and to a commercial anion exchange resin. The sorption was very rapid and the linearized pseudo-second order kinetic model fitted the data well. The sorption data were best fitted in the linearized Langmuir model. Modified pine sawdust was tested in column as well, where it maintained its ion exchange ability well for five ion exchange cycles including successful desorption cycles.
  
  PubDate: 2013-06-03T11:22:18Z
Theoretical investigation of simultaneous continuous preferential crystallization in a coupled mode
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Shamsul Qamar , Kamila Galan , Martin Peter Elsner , Iltaf Hussain , Andreas Seidel-Morgenstern
  The dynamic behavior of two coupled continuously operated crystallizers connected through exchange pipes and equipped with a fines removal system is theoretically analyzed. It is an extension of our recent work on continuous enantioselective preferential crystallization in a single vessel. A high resolution finite volume scheme is applied to solve the model in the crystal size coordinate, while an ODE-system in the time coordinate is solved by a fourth order Runge-Kutta method. The influences of different seeding and operating strategies on the process are studied systematically. To assess the quality of the process several goal functions are used, such as purity, productivity, yield and mean crystal size of the target enantiomer. Continuous and periodic seeding concepts are compared. The goal functions considered provide clear evidence about the significant potential of this new process. To prove advantages of the coupled process, corresponding results are compared with those for a single crystallizer.
  
  PubDate: 2013-05-30T10:00:51Z
Microscopic evaluation of binderless granulation in a pressure swing granulation fluidized bed
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Noor Fitrah Abu Bakar , Ryohei Anzai , Masayuki Horio
  To develop a microscopic understanding of the role of cyclic fluidization and compaction in making spherical and dense granules by Pressure Swing Granulation, numerical simulation was conducted with our private code (SAFIRE21) using realistic parameter values determined by a micro-particle interaction analyzer. The values of the spring constant and coefficient restitution obtained from this experimental measurement were 300–790N/m and 0.9 respectively. The results obtained by the discrete element method simulation showed that collision frequency and collision force in a fluidized bed were insufficient to cause deformation of the granules but were significant in shaping the granules spherically.
  
  PubDate: 2013-05-30T10:00:51Z
Agglomeration behaviour and product structure of clay and oxide minerals
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Ishmael Quaicoe , Ataollah Nosrati , William Skinner , Jonas Addai-Mensah
  Agglomeration of fine mineral particle into robust and porous granules is an essential precursor to heap leaching and valuable metal recovery from low grade lateritic ores. In this paper, isothermal, batch agglomeration behavior of selected model clay (kaolinite and smectite) and oxide (hematite and quartz) minerals which constitute the predominant host gangue phases of typical low-grade nickel (Ni) lateritic ores is investigated. Specifically, the influential role of feed particle size and mineralogy on H2SO4 binder dosage requirement and agglomeration behavior was studied. Granules of 5–40mm size range were produced within 8–14min and their mechanical/structural properties examined. The results showed that for equivalent wetting and saturation, finer feed particles required higher binder dosage and led to dry agglomerates of higher compressive strength and re-wetting stability in acidic solution than coarser feed particles. Furthermore, binder dosages required for effective agglomeration were greater for the clays than the oxide minerals. Quartz, kaolinite and smectite displayed markedly slower growth behavior in comparison with hematite. The internal micro-structural analysis showed that the pore volumes (porosities) of the oxide granules were noticeably more than those of the clay granules these increased markedly (20–30% for clays and 30–40% for oxides) upon drying due to stresses/strains resulting from particle shrinkage after solvent (water) loss. Agglomerate dry compressive strengths for kaolinite and hematite were found to be similar and greater than those for quartz and smectite whilst the corresponding re-wetting stability decreased in the order: kaolinite>quartz>hematite=smectite. These findings, which indicate that the correlation between granule mineralogy, structural and behavior is quite complex, provide a useful basis for benchmarking the agglomeration behavior and granule properties of lateritic mineral ores.
  
  PubDate: 2013-05-30T10:00:51Z
An experimental study examining the relationship between bubble shape and rise velocity
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): M. Maldonado , J.J. Quinn , C.O. Gomez , J.A. Finch
  Individual bubbles ca. 2.5mm in diameter were produced at a capillary in water containing frother, polymer or inorganic salt. Bubble aspect ratio (shape) and rise velocity were measured ca. 1.2m above the point of generation. Results suggest a unique relationship between bubble shape and rise velocity which is independent of solute type or concentration.
  Graphical abstract
  
  PubDate: 2013-05-30T10:00:51Z
Effect of packing fraction on indium tin oxide powder synthesis via a solid-phase reaction with microwave heating
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Kunihiro Fukui , Manabu Katoh , Yuta Saeki , Tetsuya Yamamoto , Hideto Yoshida
  The effect of the packing fraction of the powder layer of the starting material powder on the progress in the solid-phase reaction to produce indium tin oxide (ITO) using a microwave heating method was investigated using indium oxide and tin oxide powders; the electrical field and temperature distributions in the reactor were also numerically simulated. The electrical conductivity of the product powder is dependent on the packing fraction of the starting material and can be improved by reducing the packing fraction and increasing the air-feed to the powder layer, which increases the reaction temperature. Furthermore, reducing the packing fraction can equalize the radial disparity of the electrical conductivity since the starting material powder is fluidized and agitated by the introduction of air during microwave irradiation. These findings indicate that feeding air to the reactor increases the conversion and reaction rate and imparts radial uniformity to the reaction progress. It was also found that the simulated temperature distribution agrees qualitatively with the results of the experimental temperature measurements. The dependence of the reaction temperature on the packing fraction can be also expressed by the simulation. The simulation results suggest that the amount of heat generated per unit of powder volume can be used to evaluate the uniformity of the reaction progress and conversion to ITO.
  Graphical abstract
  
  PubDate: 2013-05-30T10:00:51Z
Inhibition of tetrahydrofuran hydrate crystal growth by tetraalkylphosphonium salts—superior performance to equivalent tetraalkylammonium salts
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Malcolm A. Kelland , Fredrik Gausland , Katsuhiko Tsunashima
  A series of tetraalkylphosphonium bromide salts have been tested as tetrahydrofuran (THF) hydrate crystal growth inhibitors at varying concentrations and temperatures. In general, the inhibition performance is better than that of tetraalkylammonium bromide salts. For example, tetra(n-butyl)phosphonium bromide is a much superior inhibitor than tetra(n-butyl)ammonium bromide. Tetra(n-pentyl)phosphonium bromide was the best phosphonium salt investigated and had a performance close to that of the best reported ammonium salt, tetra(iso-hexyl)ammonium bromide. Although we have not yet succeeded in synthesising tetra(iso-hexyl)phosphonium bromide, the improved performance of phosphonium salts with iso-hexyl groups was demonstrated by synthesising and testing a series of tri(n-butyl)alkylammonium bromides. The alkyl group was varied from 2 to 6 carbon atoms including normal- and iso-alkyl groups. The best THF hydrate crystal growth inhibition for this series was obtained when the alkyl group was iso-hexyl. These results suggest that the best tetraalkylphosphonium salts could be used as improved low dosage hydrate inhibitors, both in kinetic hydrate inhibitor formulations or as anti-agglomerants, compared to tetraalkylammonium salts.
  
  PubDate: 2013-05-30T10:00:51Z
Tetrahydrofuran hydrate crystal growth inhibition by bis-and tris-amine oxides
- Abstract: Publication date: 19 July 2013
  Source:Chemical Engineering Science, Volume 98
  Author(s): Malcolm A. Kelland
  Amine oxides are an alternative, non-ionic class of gas hydrate anti-agglomerant (AA) surfactants that are potentially more environmentally-friendly than cationic surfactant AAs. These classes of AAs work by interacting with hydrate crystal surfaces. Recently, we reported on the clathrate hydrate crystal growth inhibition of monoamine oxides using Structure II (SII) tetrahydrofuran (THF) hydrate (Kelland et al., 2012). It was determined that the best hydrate crystal growth inhibition was provided by amine oxides with n-butyl, n-pentyl or iso-pentyl groups, with tributylamine oxide being the best homofunctional trialkylamine oxide investigated. However, replacement of one butyl group with a larger group, forming the tail of an AA surfactant, lowered the inhibition significantly which could have consequences for the use of mono-amine oxides as AAs. We have now investigated bis-amine oxides and discovered that they can give even greater THF hydrate crystal growth inhibition than mono-amine oxides, particularly when the amine oxides have the correct size alkyl groups and are an optimum distance apart. The optimum alkyl group was found to be n-butyl and the optimum distance for bis-amine oxides is with a chain of 5–6 sp3 carbon atoms separating the nitrogen atoms. Alternatively, a heteroatom can be placed in this spacer chain, for example a third nitrogen atom, such as for alkylated derivatives of diethylenetriamine. These results mean that the use of bis-amine oxide surfactants could potentially lead to improved AA performance compared to mono-amine surfactants because of their greater adsorption onto hydrate surfaces. They may also act as improved synergists for polymeric kinetic inhibitors of natural gas hydrates.
  
  PubDate: 2013-05-26T09:02:18Z
Corrigendum to “A study of mixing by chaotic advection in two three-dimensional open flows” [Chem. Eng. Sci. 81 (2012) 179–190]
- Abstract: Publication date: 28 June 2013
  Source:Chemical Engineering Science, Volume 97
  Author(s): E. Saatdjian , A.J.S. Rodrigo , J.P.B. Mota
  
  PubDate: 2013-05-14T19:51:55Z
Numerical investigation of near-critical fluid convective flow mixing in microchannels
- Abstract: Publication date: 28 June 2013
  Source:Chemical Engineering Science, Volume 97
  Author(s): Lin Chen , Xin-Rong Zhang , Junnosuke Okajima , Shigenao Maruyama
  Supercritical CO2 fluid has been widely used in chemical extraction, chemical synthesis, micro-manufacturing and heat transfer apparatus, and so forth. The current study deals with near-critical CO2 microchannel mixing flow and its basic characteristics. Careful numerical investigations are carried out by solving the coupled computational fluid dynamic equations. The results show that strong near-critical vortex flows can be achieved in a relatively wide range of initial and controlling conditions in microchannels. Basic, isothermally developed flows are simulated and then used as the initial state for a heat convective simulation. After the wall heat flux is applied, the vortex mixing flow originates from the hot boundaries in microchannels with height D=100μm to 200μm, while natural convection will gradually become dominant for microchannels with D=300μm to 500μm. The current micro-mixing evolution can be ascribed to a novel type of Kelvin–Helmholtz instability. Well-correlated characteristic numbers are identified for the effective near-critical microchannel mixing cases. The vortex growth and evolution mode in microchannels are found to differ greatly from previous micro-mixing methods. Possible applications in micro-engineering/chemical process are also discussed in this study.
  
  PubDate: 2013-05-14T19:51:55Z
Effects of substituent groups and central metal ion on hydrogen adsorption in zeolitic imidazolate frameworks
- Abstract: Publication date: 28 June 2013
  Source:Chemical Engineering Science, Volume 97
  Author(s): Er-Yu Chen , Ying-Chun Liu , Tian-Yang Sun , Qi Wang , Li-Jun Liang
  Grand canonical Monte Carlo (GCMC) simulations were employed to compute the adsorption of hydrogen gas in zeolitic imidazolate frameworks (ZIFs). This set of ZIFs has the same basic structure, but different functional groups or central metal ions were substituted into the zeolitic framework. The amount of hydrogen adsorption in ZIFs is mainly affected by the effective porosity, but the substituent group may also influence the hydrogen adsorption amount. Under both low pressure and high pressure conditions, the trend in hydrogen adsorption amount is: –NO2>–CN (–Cl)>–CH3, which suggests a role for the electronegativity of the substituted functional group. Generally speaking, the higher the electronegativity, the larger the adsorption amount. However, the –C6H4 group is a special functional group with high π-electron delocalization that can greatly increase the saturated adsorption amount by ZIFs. The effect of the benzene (–C6H4 group) fused to imidazole in the large pores of ZIFs is superior relative to that in the small pores. The central metal ion, Zn(II) or Co(II), plays a negligible role in the ZIFs saturation adsorption capacity. These results may be helpful in designing and synthesizing new ZIFs with higher hydrogen uptake capability.
  
  PubDate: 2013-05-14T19:51:55Z
Flow of two consecutive Taylor bubbles through a vertical column of stagnant liquid—A CFD study about the influence of the leading bubble on the hydrodynamics of the trailing one
- Abstract: Publication date: 28 June 2013
  Source:Chemical Engineering Science, Volume 97
  Author(s): J.D.P. Araújo , J.M. Miranda , J.B.L.M. Campos
  A detailed numerical study on the interaction between two consecutive Taylor bubbles rising through vertical columns of stagnant Newtonian liquids is reported in this work. The CFD method used is based on the VOF technique implemented in the commercial package ANSYS FLUENT. Simulations were made for a large set of flow conditions, within the laminar regime, covering a range of Morton number of 4.72×10−5–104 and an interval of Eötvös number between 15 and 575. The changes in the shape of the bubbles interface were followed throughout the approach process, and the main hydrodynamic features characterizing the liquid film and the wake region of the trailing bubble were determined as the separation distance became smaller. Numerical data on the velocity ratio between the trailing and the leading bubble are presented, and two distinct regions are identified (acceleration and deceleration) in the corresponding evolution curves. The velocity ratio curves produced for several flow conditions were fitted to equations describing the acceleration and the deceleration behaviour of the trailing bubble. These equations together with the fitting parameters obtained here can be very useful to improve simulators of continuous slug flow.
  
  PubDate: 2013-05-10T11:57:41Z
Model study of sulfite oxidation in seawater flue gas desulfurization retain-->by cylindrical wetted-wall corona-streamer discharge
- Abstract: Publication date: 28 June 2013
  Source:Chemical Engineering Science, Volume 97
  Author(s): Xiaoping Wang , Zhongjian Li , Lecheng Lei
  The application of cylindrical wetted-wall discharge for wastewater treatment has been impeded by the lack of mathematical models. In this paper, a mathematical model for sulfite oxidation in seawater flue gas desulfurization by cylindrical wetted-wall corona-streamer discharge is presented. The model is expressed in terms of parameters including geometrical parameters of the reactor, physical properties of the effluent, reaction kinetic parameters and electrical parameters. Comparison of model results with experimental results at different operation factors indicates the agreement between the model and experiment results. In addition, the sulfite conversion model with reflux can be expanded from the conversion model without reflux. By selecting an appropriate reflux ratio, the desired sulfite conversion in a single reactor can be obtained.
  
  PubDate: 2013-05-10T11:57:41Z
Heat transfer in one-dimensional micro- and nano-cellular foams
- Abstract: Publication date: 28 June 2013
  Source:Chemical Engineering Science, Volume 97
  Author(s): Pavel Ferkl , Richard Pokorný , Marek Bobák , Juraj Kosek
  We investigate heat transfer in one-dimensional multi-layer models of polymer foams and determine their equivalent thermal conductivities. The proposed model considers the participating gas and solid phases, i.e., combined heat transfer by conduction and radiation in both phases and partial photon reflection on phase interfaces. A correction for possible non-Fourier heat conduction in small gas cells, occurring in nanocellular foams, is implemented by the reduction of gas thermal conductivity based on the Knudsen number. The developed model was used for the optimization of foam structure with respect to its insulation properties. We found that although radiation can account for more than one-third of the total heat flux, it can be reduced in foams with cell-sizes below 100 μ m and be almost nullified by decreasing the foam cell size to sub-micron range. The presented model is a starting point for the development of an advanced model of heat transfer in spatially three-dimensional polymer foams.
  
  PubDate: 2013-05-10T11:57:41Z
Numerical simulations of contact drying in agitated filter-dryer
- Abstract: Publication date: 28 June 2013
  Source:Chemical Engineering Science, Volume 97
  Author(s): Ekneet Kaur Sahni , Bodhisattwa Chaudhuri
  Continuum mechanics based computational methods were used to study the heat transfer and particulate flow in an agitated filter-dryer. Numerical simulations of granular flow are presented using thermal particle dynamics. A previously developed thermal particle dynamics model was modified to include the effects of interstitial fluid, and heat transfer through liquid bridges in an agitated vessel for a three dimensional granular system. Temperature, solvent concentration, and velocity profiles obtained from the simulations were used to study the effect of operational parameters (wall temperature, impeller speed, bed depth) and particle properties. Trends observed in contact drying experiments, namely the dependence of drying rate on the driving force and effect of material properties on drying behavior, have been reproduced by the model both qualitatively and quantitatively. Apart from the operational variables, frictional characteristics of model material were also found to affect the flow patterns and hence the drying kinetics. For low friction coefficients, three dimensional recirculation zones were not formed which was confirmed from the velocity profiles obtained from simulations.
  
  PubDate: 2013-05-10T11:57:41Z
Arsenic removal from groundwater by electrocoagulation in a pre-pilot-scale continuous filter press reactor
- Abstract: Publication date: 28 June 2013
  Source:Chemical Engineering Science, Volume 97
  Author(s): Omar J. Flores , José L. Nava , Gilberto Carreño , Enrique Elorza , Francisco Martínez
  We investigated arsenic removal from groundwater by electrocoagulation (EC) using aluminum as the sacrificial anode in a pre-pilot-scale continuous filter press reactor. The groundwater was collected at a depth of 320m in the Bajío region in central Mexico (arsenic 50μgL–1, carbonates 40mgL–1, hardness 80mgL–1, pH 7.5 and conductivity 150μScm–1). The influence of current density, mean linear flow and hypochlorite addition on the As removal efficiency was analyzed. Poor removal of total arsenic (<60%) in the absence of hypochlorite is due to a mixture of arsenite (HAsO2(aq) and H3AsO3(aq)) and arsenate (HAsO4 2−). Arsenic removal is more efficient when arsenite is oxidized to arsenate by addition of hypochlorite at a concentration typically used for disinfection (1mgL–1). Arsenate removal by EC might involve adsorption on aluminum hydroxides generated in the process. Complete arsenate removal by EC was satisfactory at a current density of 5mAcm–2 and mean linear flow of 0.91cms–1, with electrolytic energy consumption of 3.9kWhm3.
  
  PubDate: 2013-05-10T11:57:41Z